# Exam Practice

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```					Dr. Jay Brown                                             Name: ____________________
Statistics- Psy 2420-01                                 Practice Exam 2, Summer 2009

There are 20 multiple choice questions on the real test worth 40 points, use the study guides to

21. Which of the following will increase the power of a statistical test? (Check correct alternative
for each item).

a. _____ decrease _____ increase          The probability of a Type I error.

b. _____ decrease _____ increase          The size of the experimental effect.

c. _____ decrease _____ increase          The population variance.

d. _____ decrease _____ increase          The probability of a Type II error.

e. _____ decrease _____ increase          The sample size (n).

f. _____ choose a one-tailed test _____ choose a two-tailed test.

22. If random samples of size n are drawn from a normal population having a mean  = 80 and
standard deviation X = 12.

a. What proportion of samples with n = 9 will have means between 74 and 86?

b. What proportion of samples of size n = 32 will have means greater than 83?

c. What proportion of samples of size n = 16 will have means between 77 and 82?

23. Scores on a course exam are normally distributed with  =80 and X = 8. The teacher wants
to give the top 20% of the class “honors”, a grade of “fail” to the bottom 30%, and the grade of
“pass” to the remaining 50%. What examination scores should be used as the boundaries for

“Fail” X  __________              “Honors” X  __________

24. A researcher examines the effects of sleep deprivation on people’s moods. On one day, the
researcher allows n = 9 subjects to sleep until they wake (no sleep deprivation). The subjects
are then presented with a questionnaire which asks them to rate how good they feel (a high
score indicates a good mood, a low score indicates a bad mood). The following night the
researcher forces these same nine people to stay awake all night. The following morning they
are again presented with a questionnaire which asks them to rate how good they feel. The data
are as follows:

Full nights sleep            Sleep deprived         D (sleep – no sleep)
10                         4                6
7                          5                2
8                          3                5
4                          7                -3
8                          2                6
2                          5                -3
7                          6                1                    D = 20
D = 140
2
6                          4                2
9                          5                4

Did sleep deprivation cause mood scores to be lower? Test with = .01.

a. State the appropriate statistical hypotheses

H0:_______________            vs      Ha:_______________

b. Write the formula for the appropriate test statistic:

c. What is/are the critical value(s) for your test statistic?

d. For these data, what is the obtained value of the test statistic?

e. Your decision (Based on the H0 and in words):

25. A researcher knows that the average weight of American men between 30 and 50 is  = 162
pounds with X = 28. The researcher would like to determine if men who have heart attacks
between those ages are heavier than the average male. For a random sample of 25 heart
patients, body weights are recorded. The sample mean is X = 174 and the standard deviation is
SX = 24. Are these patients significantly heavier than the population? Test with  = .01.

a. State the appropriate statistical hypotheses

H0:_______________            vs      Ha:_______________

b. Write the formula for the appropriate test statistic:

c. What is/are the critical value(s) for your test statistic?

d. For these data, what is the obtained value of the test statistic?

e. Your decision (Based on the H0 and in words):

26. An industrial/organizational psychologist wants to know if there is a relationship between
experience and worker productivity. He goes to the Ford factory and asks to see the
employment records of the people working on the fender assembly line. The researcher looks in
the records and finds the number of years each worker has been employed and the number of
fenders that they assemble per hour.

Years on Job (X)    Fenders per hour (Y)
12                 18                          X = 176
25                  20                         Y = 185
37                 21                          X2 = 5608
2                  12                          Y2 = 3995
32                 26                          XY = 3849
8                  29                          n=9
0                  19                          SY2 = 21.358
47                 22
13                 18

a. What is the correlation between these variables?

__________
b. Before I know anything else, how many fenders per hour should I predict for the next
person?

__________
c. After I find that the next person has been working at Ford for 23 years, how many
fenders per hour should I predict for that person?

__________
d. Upon making the prediction in Part C, how much error should I expect (on average) I

__________
e. What proportion of variance in fenders per hour does years on the job account for?

__________

27. A developmental psychologist would like to know if there is a difference in the vocabulary
development of 6-year-old boys and 6-year-old girls. Random samples of n = 4 boys and n = 6
girls are given a standardized vocabulary test. The following data represent their scores:
Boys                  Girls
82                     98                           n1 = 4
76                     78                           n2 = 6
65                     89                           SS1  158 .55
78                     93                           SS 2  643
90                           X 1  75 .25
67                           X 2  85 .83

Using  = .05, test whether 6-year-old boys are different from 6-year-old girls on this
standardized vocabulary test.

a. State the appropriate statistical hypotheses

H0:_______________            vs      Ha:_______________

b. Write the formula for the appropriate test statistic:

c. What is/are the critical value(s) for your test statistic?

d. For these data, what is the obtained value of the test statistic?

e. Your decision (Based on the H0 and in words):

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